This invention relates to a power working machine such as a chain saw.
A power working machine, e.g., a chain saw has a main body case cover, a rear handle disposed on a rear portion or upper central portion of the main body case cover, and a front handle extending from its upper front portion to its lower portion on one side along a side surface of the main body case cover. The rear handle is gripped by one hand of the operator to support the main body case, while the front handle is gripped by the other hand of the operator and is used to correctly direct and position the saw chain guide bar of the chain saw to the cutting position on an object such as standing tree or timber as well as to apply a force for cutting the object downward to the saw chain guide bar. The front handle of this type of conventional chain saw is formed of a pipe having a circular sectional shape and therefore tends to slip on the operator's hand when gripped by the operator. It is therefore necessary for the operator to firmly grip the front handle and force the same downward to apply the cutting-down force to the saw chain guide bar. Problems are thereby encountered in that the operator tends to have a pain in his hand and to be soon fatigued, and that it is not possible to use a slender pipe to reduce the size and weight of the main body case.
Ordinarily, the prime mover is fixed to the main body case in a predetermined portion therein at the time of assembly by being screwed to the main body case by means of bolts inserted in holes or cutout portions formed in the main body. Thus, in conventional power working machines such as chain saws, holes and cutout portions through which bolts and the like are inserted are formed in the main body case and are exposed to the outside. There is therefore a risk of foreign materials such as dust and rain water entering the main body case, resulting in damage or deterioration in the internal devices and, hence, a reduction in the life of the machine. Also, the exposed holes and cutout portions in the main body case impair the appearance of the machine and reduce the value of the same in the market.
Moreover, in conventional chain saws, a prime mover such as an air-cooled two stroke cycle internal combustion engine is housed in the main body case and is fixed to the same. For mounting the engine, screw holes are formed in the crank case of the engine, screws are inserted into these screw holes by being passed through holes formed in the main body case and are screwed to fix the engine to the main body case. It is therefore necessary to align the screw holes of the crank case and the main body case with accuracy at the time of assembly, which operation is troublesome and increases the assembly time, and a strict tolerance for working the screw holes is also required It is also necessary to adopt a forming method and a high-class plastic material which satisfy conditions for avoiding any deformation of the main body case when the same is formed. The manufacturing cost is thereby increased.